Septoria leaf spot is caused by a fungus, Septoria lycopersici and is one of the most destructive diseases of tomato foliage.
Infection can occur at any stage of plant development.
It is sometimes mistaken for early blight in tomatoes, and vice versa.
Septoria leaf spot can affect many parts of tomato plants, commonly causing leaf spots and stem lesions.
Long periods of high relative humidity, temperatures of 60–80 degrees F, and leaf wetness are ideal conditions for development and spread of the pathogen.
Life Cycle
Although the fungus is not a soil inhabitant, it overwinters on infected tomato debris incorporated in soil or on weeds in solanaceous family like nightshade. It can also survive on equipment such as plant stakes and cages.
Spores may be spread by windblown water, splashing rain, hands and clothing of pickers, insects such as beetles, and cultivation equipment. They may germinate within 48hours under moist conditions and favorable temperatures.
Leaf spots can appear within 5 days, pycnidia appear within 7-10 days, and spore production is repeated within 10-13 days.
Tomato seed have been shown to carry spores and produce infected seedlings.
Infection & Symptoms
Septoria leaf spot first appears on the lower/older leaves. The disease then spreads upwards from the oldest to the youngest growth.
The spots are circular, with dark brown margins and tan to gray centers with small black fruiting structures. Characteristically, there are many spots per leaf.
In the center of the spots are many dark brown, pimple-like structures called pycnidia-fruiting bodies of the fungus. These structures are large enough to be seen with the unaided eye or with the aid of a hand lens.
Spots may also appear on stems, calyxes, and blossoms, but rarely on fruit.
Heavily infected leaves will turn yellow, dry up, and drop off. This defoliation results in sun-scalding of the fruits.
Septoria leaf spot does not show characteristic “target” or concentric spots as seen in early blight.
Control
Chemical control
The following fungicides are recommended for prevention and eradication of Septoria leaf spot.
- RANSOM 600WP 15g/20l
- DOMAIN 250EC 10ml/20l
- BRADLEY 500SC 10ml/20l
- DUCASSE 250EC 20ml/20l
- EXEMPO CURVE 250SC 15ml/20l
- MEGAPRODE LOCK 525P 30g/20l
- MILLIONAIRE 690WDG 40g/20l
- PROVIDENCE 400WP 50g/20l
- ABSOLUTE 375SC 10ml/20l
Note
- Whenever spraying any fungicide, it is advisable to mix it with INTEGRA 3ml/20l, which improves the efficacy of the respective fungicide. It is a sticker, spreader, wetter and penetrant.
- Timely application of fungicides is very critical for effective control of the disease.
- In order to prevent resistance build-up over any of the fungicides by the fungus, it is recommended that several fungicides be alternated throughout the crop season.
Non-chemical methods
- Remove and burn the diseased plant materials. Do not compost them
- Use resistant varieties
- Use certified or disease-free planting materials
- Maintain field sanitation/hygiene
- Improve air circulation around the plants.
- Mulch around the base of the plants. This reduces splashing soil, which may contain fungal spores associated with debris.
- Avoid overhead irrigation because it facilitates infection and spreads the disease.
- Control weeds, especially those in the same family with tomato like Nightshades
- Crop rotations with non-hosts
- Plant tomatoes in a raised bed to improve drainage and prevent diseases from spreading
